This invention relates to a mixer valve comprising a valve body, control means, a changeable cartridge inserted into the valve body, a hard material fixed plaque mounted in said cartridge, and at least one movable plaque housed in said cartridge, connected to the control means and intended to cooperate with said fixed plaque for carrying out the regulation of the flow rate and the mixing ratio.
To be capable of carrying out an effective closure, the fixed and movable plaques of the mixer valves of the type referred to must be pressed one against the other with an adhesion force proportionate to the pressure of the incoming water, because otherwise the pressure of the water would separate the plaques from one another, thus preventing the closure. The force which keeps the plaques pressed one against the other is usually provided by a spring or by the resiliency of one or more sealing gaskets disposed between the fixed plaque and the valve body. This force must be of such a high value as to be able to support the maximum pressures expected, and even, in particular, the high pressures which are applied in certain conditions of testing, in compliance with the provisions of the laws, and which are much higher than the normal operation pressures. The same high adhesion force is then applied onto the plaques also in the normal operation conditions, thus generating frictions which render unnecessarily difficult the operation of the valve and subjecting the parts of the valve to unnecessary stresses.
Since the spring, or the compressed gasket, has to provide a high adhesion force between the plaques, it must be compressed energically when applying the cover to the valve body, and therefore the cover must be connected to the valve body by means of screws or being screwed itself, thus requiring the use of tools for the application and the removal of the cover and consequently, in particular, for changing the cartridge.
Moreover, the sealing gasket disposed between the fixed plaque and the valve body is usually intended to also compensate for the working tolerances, as well as the thermal expansions to which the cartridge is subjected during the operation, and therefore it must have a considerable free thickness. Accordingly, in case of high pressure differences between the water inlet pipes, and even more in case of pressure shocks, said gasket may be deformed or expelled from its seating, thus rendering unusable the valve.